Process of manufacturing electron-emitting cathodes



July 7, 1925. 1,545,256

c. D. HOCKER PROCESS OF MANUFACTURING ELECTRON EMITTING CATHODES Filed Sept. 5 1918 //7 venfan' Car/ Z76 W/f/ f/oc/rek y 'Af/j Patented July 7,- 1925,

UNITED. STATES PATENT OFFICE.

CARL D. HOOKER, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PROCESS OB MANUFACTURING ELECTRON-EMITTING OATHODES Application filedSeptember 5, i918. Serial No. 252,689.

To all whom it may concern: 7

' siding at East Orange, in the county of Essex and State of New Jersey, have'inve'nted certain new and useful Improvements in the Process of Manufacturing Electron-Emittin Cathodes, of which the following is a fuli clear, concise, and exact description.

This invention relates to the process of manufacturing electron-emitting cathodes, such as are used in audions or vacuum tubes.

It has been known for some time that the thermionic activity of a metal, for example platinum, may be greatly increased, by applying a coating of compounds of alkaline earth metals thereto.

An object of the present invention is to provide a convenient manner of applyin the thermionically active coating materia upon a filamentary cathode.

As disclosed in the .patent to Nicolson and Hull, No. 1,209,324,'December 19, 1916, Electron-emitting cathode and the process of manufacturing the same, the coating material may be a plied to the filament by diping a heated lament into troughs containmg strontium hydroxide and barium resinate. In the then preferred process of carrying out the invention, the strontium hydroxide, which is only sparingly soluble, is made into a thin paste'with water before being applied to the filament, and due to the tendency of this compound to settle out of suspension, 'it is necessary to stir the solution at frequent intervals.

This difliculty of keeping the material in sus ension while coating the filament is avoided, accordin to the present invention, the coating materlal being embodied or suspended in a solid'carrier which may be of waxy material such as parafiin.

Other advantages to be derived by the use of a solid or wax-like material as a carrier are:

1. Saving of material incorporated in the carrier sincethe wax-like carrier does not spill or run away as is characteristic of the water suspension.

2. Thorough protection of the material incorporated 1n the wax from the action of carbon d 1ox1de, water, or other constituents of the air that might change its character. This makes it possible to em loy the waxllke coating mixture, even a r an indefinlte length of standing. 3. Saving of time in application of'coatmg. 1

According to the present invention, it is preferred to use the carbonates-of barium and strontium, the desired quantity of each of which is stirred into separate batches of molten paraflin which is stirred until cool and then formed into the desired shape, for lnstance, in the shape of rods or other convenient form. a

An advanta e to be-derived from using -carbonates rather than oxides of alkaline earth metals is that the carbonates are more easily prepared. pure and with more assurance o uniformity than the oxides or hydroxides. In the preparation of the latter, a troublesome calcining operation is necessary.

The filament core which is preferably of latinum is heated in the usual way to a sufcient temperature to, melt the paraflin as it is move along the hot wire. It is preferred that a total of sixteen coats of the carbonate should be ap lied in the following way: 4 coats of Sr 61,4: coats ofBaCO 4 coats of SrCO,, 4 coats of BaCO,. Between the a plication of each coating-the wire should flashed to a red heat, which serves to burn off the parafiin, reducing the alkaline earth compound to an oxide which adheres closely to the filament.

Fig. 1 illustrates diagrammatically apparatus that may be employed for coating the filament.

Fig. 2 of the drawing illustrates a vacuum tube of the audion type the cathode 1 of which is made in aceo ance with the above process.

Referrin in detail to Fig. 1, the filament.

1 to be use as a cathode, may be twisted as in VViile the filament is heated, the rod 5 which com rises a solid carrier in' which is embodied coating material, as indicated above, passes along the length of the wire 2, the solid carrier melting and depositmg the coating material on the filament. 'In case strontium and barium compounds are used as coating materials, it is preferred that only one of these in the form of a carbonate .should be embodied in one rod 5 which may be of araifine, while the other carbonate is. emb led in a se arate rod of parafiine. Good results may e obtained, however, by

' embod ing both carbonates in a single rod.

A fii' ament made in accordance'with the process indicated above having aplatmum core and multiple layers of .strontlum and barium compounds should preferably finally baked in air about two hours. It is not necessary that the partlcular coating material indicated above should be em lo ed,- as;-any suitable material may be em led in the carrier, which, being in a solid; form, aifords 'a very convenient manner of applying the coating. material to the filament. Moreover, it is not essentlal that platinum as indicatedv above should be ,employed as the filament core, for any other suitable material, such as nickel wh1ch has given good results, may be used.

What is claimed is:

1. A carrier solid at ordinary tem eratures and capable of being melted at higher temperatures, and thermionically active coating material embodied in' said carrier.

2. A carrier, solid at ordinary tem eratures and capable of being melted at higher temperatures, and thermionically active coating material mechanically mixed with said carrier.

'3. A carrier of waxy material solid at ordinary tem eratures and capable of being melted at hig er temperatures, anda thermionically active alkaline earth metal compound embodied therein.

4. A carrier of arafiine and a carbonate of an alkaline eart metal embodied therein.

5. A carrier of waxy material, andacarbonate of an alkaline earth metal embodied therein.

6. The method of which com rises heatln said filament, in coating sai filament wit parafilne containing a compound of an alkaline earth metal,

and in baking said coat to an electrical conductor preparing a filament plym 7. The method of preparing an electrode adapted to serve as a source of electrons which comprises coatin said electrode with metal, and

fusible carrier having a com ound of an alkaline earth metal embodied t erein.

10. The method of making a thermionically active filament which comprises applying to said filament while slightly heated a readily fusible carrier havin a carbonate of an alkaline earth metal embodiedtherein.

11. The method of making a thermionically active filament which comprises coating said filament with a readily fusible carrier having thermionically active coating material embodied therem.

12. The method of making a thermionically active filament which comprises coat- ;ing said filament with a readily fusible carrier having a compound of strontium embodied therein.

13. The method of making a thermionically active surface which comprises coa it with a material containing a thermiom cally active substance, said material being solid at ordinary temperatures and capable ofbeing melted at higher temperatures.

14. The method of making a thermioni-- cally active filament which comprises coating said filament a plurality oftimes with a readily fusible carrier having embodied therein thermionically active coating material.

15. The method of making an electron emitting electrode which comprises applying while slightly heated a readily fusible carrier having embedded therein a coatin containing a metal of thealkaline grou akin said coating; then applying a rea 'ly fusib e carrier comprising a coating containing another metal of the alkaline earth group; and baking said coatin 16. e method of making an electron emitting electrode which comprises ap lying to an electrical conductor while s ghtly heated a readily fusible carrier having embedded therein a compound of strontium, and in baking said coating.

17. The method of manufacturing an electron emitting electrode which comprises a .to an electrical conductor w e slight y heated multiple coatings of strontium and barium comgpunds which are embedded a readily sible carrier and in baking and coatings.

18. The method of making an electron emitting electrode which comprises coating platinum with alternate coatin of strontium and barium compounds em edded in a 5 readily fusible carrier, the strontium coating being applied first to the platinum, the barium coating being applied subsequently, and in baking said coatmgs.

19. The method of making an electron 10 emitting electrode which comprises coating platinum with alternate coatings of strontium carbonate and barium carbonate embedded in a readily fusible carrier, and in baking said coatings in air for about two hours.

In witness whereof, I hereunto subscribe my name this 30th day of August A. D., '1918.

CARL D. HOOKER. 

